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diff --git a/devtools/client/shared/WeakMapMap.js b/devtools/client/shared/WeakMapMap.js
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+++ b/devtools/client/shared/WeakMapMap.js
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+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+/**
+ * WeakMapMap is a weakmap collection dual-keyed using an object and a string.
+ * This is useful for keeping data compartmentalized e.g. grouped by tab.
+ *
+ * It's name comes from the internal structure which maps a WeakMap to a map,
+ * which contains the target data.
+ *
+ * Usage:
+ *   const myWeakMapMap = new WeakMapMap();
+ *   const key = { randomObject: true };
+ *   myWeakMapMap.set(key, "text1", "Some value1");
+ *   myWeakMapMap.set(key, "text2", "Some value2");
+ *   myWeakMapMap.get(key, "text1"); // Returns "Some value1"
+ *   myWeakMapMap.get(key, "text2"); // Returns "Some value2"
+ *   myWeakMapMap.has(key, "text1"); // Returns true
+ *   myWeakMapMap.has(key, "notakey"); // Returns false
+ */
+
+"use strict";
+
+class WeakMapMap {
+  constructor() {
+    this.clear();
+  }
+
+  /**
+   * Returns the value associated to the key and nestedKey, or undefined if
+   * there is none.
+   *
+   * @param {Object} key
+   *        The key associated with the desired value.
+   * @param {String} nestedKey
+   *        The nested key associated with the desired value.
+   */
+  get(key, nestedKey) {
+    if (!this.has(key, nestedKey)) {
+      return undefined;
+    }
+
+    return this.store.get(key).get(nestedKey);
+  }
+
+  /**
+   * Returns the value associated to the key and nestedKey, or undefined if
+   * there is none.
+   *
+   * @param {Object} key
+   *        The key associated with the desired value.
+   * @param {String} nestedKey
+   *        The nested key associated with the desired value.
+   */
+  has(key, nestedKey) {
+    const hasKey = this.store.has(key);
+
+    return hasKey && this.store.get(key).has(nestedKey);
+  }
+
+  /**
+   *
+   * @param {Object} key
+   *        The key associated with the value.
+   * @param {String} nestedKey
+   *        The nested key associated with the value.
+   * @param {any} value
+   *        The value to add.
+   */
+  set(key, nestedKey, value) {
+    if (!this.store.has(key)) {
+      this.store.set(key, new Map());
+    }
+
+    const innerMap = this.store.get(key);
+    innerMap.set(nestedKey, value);
+  }
+
+  /**
+   * Removes the value associated to the key and nestedKey.
+   *
+   * @param {Object} key
+   *        The key associated with the desired value.
+   * @param {String} nestedKey
+   *        The nested key associated with the desired value.
+   *
+   * @returns True if an element in the store has been removed successfully.
+   *          False if the key is not found in the store.
+   */
+  delete(key, nestedKey) {
+    if (!this.store.has(key)) {
+      return false;
+    }
+
+    return this.store.get(key).delete(nestedKey);
+  }
+
+  /**
+   * Clear the store.
+   */
+  clear() {
+    this.store = new WeakMap();
+  }
+}
+
+module.exports = WeakMapMap;